I hope this helps to clear things up. Ancestry DNA testing is not an exact science, and is limited by the fact that we don't inherit the exact same DNA our parents had, meaning that with each new generation, old DNA is lost. Ancestry tests can provide estimations of our genetic ancestry, and though they are improving all the time, they can't tell the whole story of our heritage.
In fairness to 23andME, it leaves it up to the customer to unlock the more serious results – or not. When I unlock mine, I discover that, while I’m not genetically predisposed to such things as the BRAC1 or BRAC2 variant, Parkinson’s or MS, I have one of the variants for late-onset (mid-80s) Alzheimer’s. However, I don’t have any other markers for Alzheimer’s or family history or conditions associated with it or anything else listed in the rather lengthy disclaimer, which also stresses that it’s not a diagnostic result and to seek further advice from your GP if you are concerned.
FTDNA is the market leader for both Y-DNA and mtDNA testing, and has the world’s largest Y-DNA and mtDNA genealogical matching databases. They are the only company that allows complete integration of Y-DNA, mtDNA and autosomal DNA test results for genealogical purposes. They host a wide variety of surname projects, haplogroup projects (Y-DNA and mtDNA), and geographical projects. Experienced and knowledgeable volunteer project administrators can often provide advice and help with the interpretation of results. They are not the first choice for autosomal DNA because of the smaller database but matches are more likely to be responsive and interested in genealogy.
1. Family Tree DNA’s Family Finder: One of the first to offer these types of tests, FTDNA is generally considered the leader in autosomal DNA testing for ancestry and provides some of the best tools available for genealogists. Their population finder section is currently a bit less specific than the other companies, but FTDNA Family Finder users are eagerly awaiting a much improved update to be released sometime in the next month. Find out about Family Finder here.